1. Field of the Invention
This invention relates to a reactor/mixer design and process for an alkylation process wherein C3, C4 and C5 olefins are reacted with isobutane to produce alkylate in the presence of sulfuric acid catalyst. In one embodiment the invention more particularly relates to a process and apparatus wherein an eductor is used in lieu of mechanical mixer to mix the sulfuric acid and hydrocarbons. In another embodiment more particularly the invention relates to a process wherein new the C3/C4 vapors from the auto refrigeration may be used in lieu of refrigeration compression. Finally in a third embodiment successive coalescing devices are used to remove the acid from the hydrocarbon to ppm level.
2. Related Information
The conventional sulfuric acid catalyzed alkylation process has been practiced in the past using mechanical propeller mixers which require complex seals. The internal mixer and seals are subjected to a hostile environment (strong sulfuric acid which is used as catalyst for the process) which is demanding. To provide the mixing and tight emulsion required for the process considerable energy is necessary for each contactor/reactor. The impellers/seals used require considerable maintenance. To facilitate the mixing conventional processes are carried out at temperatures so as to keep the viscosity low, and these temperatures are not optimum temperatures to make high octane product with low acid consumption. The operating expense of the conventional process together with complicated mixing device which has been known to require higher maintenance can be reduced.
The alkylate product in the refinery economics of gasoline, normally has very good return on investment based on the conventional process, but still the units require high investment, maintenance and liquid waste disposal. The hydrofluoric acid (HF) alkylation does not require refrigeration and acid regeneration so it is marginally better in that respect, but due to the high corrosive nature of the HF acid, exotic materials of construction are required. The process is also much more hazardous due to the HF acid, and is not readily acceptable environmentally.
Mixing devices for mixing the hydrocarbons and acids have been variously disclosed in U.S. Pat. Nos. 5,443,799; 3,696,168; 3,133,128; 4,000,212; 3,758,613 and 5,220,094. All of these patents disclose mixing devices with spray nozzles/spargers/venturi which are all low efficiency mixing equipment options and in most cases have been applied to HF Alkylation which have better reaction kinetics than sulfuric acid alkylation. The art listed in the above referenced patents does not meet the hydrodynamic requirements of an eductor with divergent portion after the nozzle. The previous art is a mixture of spray nozzles/spargers and venturi devices that produce mild mixing and are not suitable for sulfuric acid alkylation high efficiency mixing requirements. Spray nozzles and spargers do mix the liquid but they doe not provide the high efficiency as provided by an eductor. As noted, most of these earlier patents have been for HF Alkylation, though some are broad in sense but as these are do not provide the same efficiency and hydrodynamics, they cannot be accept as equivalent to eductors due to major hydrodynamics differences.
The vapor from this flash drum can be sent to an absorption column or to a compressor intermediate stage, or if the flash is done at higher pressure it can be condensed separately and recycled to the reactor with olefin feed and isobutane
Due to the side reactions taking place in the process due to the impurities, acid soluble oils (ASO) which are conjunct polymers, are produced which reduce the acid concentration and fresh acid make up is needed to overcome this loss. The acid soluble oil is sent to the acid regeneration unit. The cost of acid regeneration for low acid consumption unit is about 20% of the operating cost of the alkylation unit.